Comparative Pharmacokinetics and Metabolic Pathway of Gemcitabine During Intravenous and Intra-arterial Delivery in Unresectable Pancreatic Cancer Patients

Patients and methods: Seven patients with unresectable pancreatic cancer received escalating intra-arterial doses of gemcitabine ranging from 800 to 1400 mg/m², after selective embolisation of all pancreatic blood supply, except for the tumour-feeding arteries. Four patients received intravenous gemcitabine (control). Venous blood samples at different time intervals were taken throughout 270 minutes for pharmacokinetic analyses of gemcitabine and its inactive metabolite 2′-2′-difluorodeoxyuridine (dFdU).

Results: Pharmacokinetic data revealed differences in plasma concentrations between intra-arterial and intravenous delivery routes. The plasma concentration-time curve of gemcitabine during and after cessation of intra-arterial pancreatic target administration through the proximal splenic artery showed a profile with an area under the plasma concentration-time curve from 0 to 270 minutes (intra-arterial 29.0 + 0.4 vs intravenous 331.0 + 2.7 ng · min/mL; p < 0.0001) and peak plasma concentration (intra-arterial 1.1 + 0.2 vs intravenous 7.6 + 2.0 ng/mL; p < 0.0001) significantly lower than that for the corresponding systemic intravenous route. A plot of In (% of dose) versus time showed a bi-compartmentalised metabolic model for intravenous administration of gemcitabine, one indicating rapid conversion of gemcitabine to dFdU, and another at a significantly lower affinity resulting in no conversion. Hence, this could be the main reason why dFdU was not detected in the systemic circulation during pancreatic intra-arterial target delivery. Furthermore, during intravenous administration a pseudo first-order rate constant (≈0.20 min^-1) for in vivo conversion of gemcitabine to dFdU was estimated, indicating a rapid cellular deamination which was not shown in the intra-arterial route. Clinically, one patient had a partial response and six patients had a stable disease after intra-arterial administration of gemcitabine. The median time to disease progression was 4 months and the median overall survival was 5 months. One patient survived for 26 months. No grade III or IV toxicity was documented.